Comment 7 for bug 239277

Window managers cannot assume window boundaries based on struts when the programs themselves do not set struts. AWN doesn't set struts when displaying in 'flat' mode and thus Openbox or any other WM can't use them.

The true cause of the problem is that Openbox reparents undecorated windows inside a frame window of its own creation. Doing so causes the frame window to receive the events rather than the window behind the frame.

I've filed a bug against Openbox at http://bugzilla.icculus.org/show_bug.cgi?id=3799 describing the issue.